Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C21/00—Treatment of glass, not in the form of fibres or filaments, by diffusing ions or metals in the surface
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
  • C03C3/093—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium containing zinc or zirconium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
  • C03C4/18—Compositions for glass with special properties for ion-sensitive glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2204/00—Glasses, glazes or enamels with special properties
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension

Definitions

• the invention relates to silicate glasses. More particularly, the invention relates to silicate glasses in which the content of non-bridging oxygen atoms in the glass is minimized. Even more particularly, the invention relates to such silicate glasses that are scratch resistant and less susceptible to edge chipping.
• Glass has the drawback of being brittle.
• Brittleness is generally is understood to be the ratio of the hardness divided of the glass to its fracture toughness. Such brittleness leads to breakage, defects, and edge chipping, all of which are particularly problematic in applications such as cover plates for mobile electronic devices, touch screens, watch crystals, solar concentrators, windows, screens, containers, and the like.
• Glass compositions having higher toughness are less brittle, resist crack propagation, and are less prone to other types of damage, such as edge chipping.
• Softer (i.e., less hard) glasses are less brittle, but are less scratch resistant.
• the present invention provides silicate glasses with improved resistance to scratching and edge chipping.
• the glasses not only maximize toughness, but allow maximization of hardness without impacting brittleness.
• the glasses are ion exchangeable and down-drawable.
• the glasses may be used for cover glasses for mobile electronic devices, touch screens, watch crystals, solar concentrators, windows, screens, and containers, as well as other application that require a strong, tough glass.
• one aspect of the invention is to provide a silicate glass.
• the silicate glass comprises at least one of alumina and boron oxide, and at least one of an alkali metal oxide and an alkali earth metal oxide, wherein -15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) - B 2 O 3 ⁇ 4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is one of Mg, Ca, Sr, and Ba.
• a second aspect of the invention is to provide an aluminoborosilicate glass.
• the aluminosilicate glass has a toughness in a range from about 0.7 MPa m 0 5 up to about 1.2 MPa m 0 5 and brittleness of less than about 8.5 ⁇ m '0 5 .
• a third aspect of the invention is to provide a silicate glass.
• the silicate glass comprises: at least one of alumina and boron oxide; and at least one of an alkali metal oxide and an alkali earth metal oxide, wherein —15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) - B 2 O 3 ⁇ 4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is one of Mg, Ca, Sr, and Ba, and wherein the silicate glass has a toughness in a range from about 0.7 MPa m 0 5 up to about 1.2 MPa m 0 5 and a brittleness of less than about 8.5 ⁇ m " ° 5 .
• a fourth aspect of the invention is to provide a cover plate for an electronic device.
• the cover plate comprises a silicate glass.
• the silicate glass comprises at least one of alumina and boron oxide and at least one of an alkali metal oxide and an alkali earth metal oxide, wherein -15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) - B 2 O 3 ⁇ 4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is one of Mg, Ca, Sr, and Ba.
• a fifth aspect of the invention is to provide an aluminoborosilicate glass.
• FIG. 1 it will be understood that the illustration is intended for the purpose of describing a particular embodiment of the invention and is not intended to limit the invention thereto.
• Glass has the drawback of being brittle. Brittleness leads to the problems of breakage, defects, and edge chipping.
• the brittleness of a material is often referred to in the art as the ratio of the hardness of the material to its fracture toughness. Glasses having a higher degree of toughness are therefore less brittle and have a greater resistance to crack propagation and scratching.
• the present invention provides a silicate glass having high toughness and lower brittleness.
• the silicate glass comprises at least one of alumina (Al 2 O 3 ) and boron oxide (B 2 Os) and, in one embodiment, comprises both alumina and boron oxide.
• the silicate glass comprises at least one of an alkali metal oxide (also referred to herein as an "alkali oxide”) having the general formula R 2 O and an alkali earth metal oxide (also referred to herein as an "alkali earth oxide”) having the general formula R'O, where -15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) - B 2 O 3 ⁇ 4 mol%, wherein R 2 O, R'O, Al 2 O 3 , and ZrO 2 represent the amounts or concentrations of the respective oxides expressed in mol%.
• an alkali metal oxide also referred to herein as an "alkali oxide”
• an alkali earth metal oxide also referred to herein as an "alkali earth oxide” having the general formula R'O, where -15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) - B 2 O 3 ⁇ 4 mol%
• alkali metal refers to the Group IA metals lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs)
• alkali earth metal refers to the Group IIA metals magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).
• concentrations of the components of the glass are expressed in mole percent (mol%).
• the silicate glasses described herein are glasses in which non-bridging oxygen atoms (NBOs) have been minimized to increase the toughness of the glass.
• NBOs non-bridging oxygen atoms
• NBOs typically decreases the melting temperature of the glass, thus facilitating melting, especially without the use of toxic fining agents such as As 2 O 3 and Sb 2 O 3 .
• Such modifier-rich glasses i.e., glasses having relatively high concentrations of R 2 O and R'O
• glasses having relatively high concentrations of R 2 O and R'O also have low toughness and high hardness and are hence quite brittle.
• the silicate glass does not comprise B 2 O 3 (i.e.,
• B 2 O 3 O mol%) and -15 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) ⁇ 4 mol%. In another embodiment, -5 mol% ⁇ (R 2 O + R'O - Al 2 O 3 - ZrO 2 ) ⁇ 4 mol%. In these instances, the number — or concentration — of NBOs is minimized by balancing the alkali and alkali earth oxides with alumina and zirconia alone.
• the addition of B 2 O 3 to these modifier-rich glasses associates with - or "ties up" - the NBOs with B 3+ ions.
• the NBOs are converted to bridging oxygen atoms through formation of BO 4 tetrahedra, resulting in a glass that is tougher and still easy to melt.
• the silicate glass has a toughness in a range from about 0.7 MPa m 0 5 up to about 1.2 MPa m 0 5 .
• the toughness is in a range from about 0.8 MPa m 0 5 up to about 1.0 MPa m 0 5 .
• the silicate glass has a hardness in a range from about 6 GPa up to about 8 GPa. As previously described, brittle ness is defined as the ratio of toughness to hardness. In one embodiment, the silicate glass has a brittleness of less than about 8.5 ⁇ m ⁇ 0 5 . In another embodiment, the silicate glass has a brittleness of less than about 7 ⁇ m "0 5 .
• liquidus viscosity refers to the viscosity of a molten glass at the liquidus temperature, wherein the liquidus temperature refers to the temperature at which the very last crystals melt away as temperature is increased from room temperature.
• the liquidus viscosity is at least 100 kilopoise (kpoise).
• the liquidus viscosity is at least 160 kpoise, and, in a third embodiment, the liquidus viscosity is at least 220 kpoise.
• the fusion draw process uses a drawing tank that has a channel for accepting molten glass raw material.
• the channel has weirs that are open at the top along the length of the channel on both sides of the channel.
• the molten glass overflows the weirs. Due to gravity, the molten glass flows down the outside surfaces of the drawing tank. These outside surfaces extend down and inwardly so that they join at an edge below the drawing tank. The two flowing glass surfaces join at this edge to fuse and form a single flowing sheet.
• the fusion draw method offers the advantage that, since the two glass films flowing over the channel fuse together, neither outside surface of the resulting glass sheet comes in contact with any part of the apparatus. Thus, the surface properties of the glass sheet are not affected by such contact.
• the slot draw method is distinct from the fusion draw method.
• the molten raw material glass is provided to a drawing tank.
• the bottom of the drawing tank has an open slot with a nozzle that extends the length of the slot.
• the molten glass flows through the slot/nozzle and is drawn downward as a continuous sheet therethrough and into an annealing region.
• the slot draw process provides a thinner sheet, as only a single sheet is drawn through the slot, rather than two sheets being fused together, as in the fusion down- draw process.
• the silicate glass comprises 62-70 mol.% SiO 2 ; 0-18 mol% Al 2 O 3 ; 0-
• the silicate glass is an aluminoborosilicate glass: i.e., the glass comprises both alumina and boron oxide.
• the aluminoborosilicate glass comprises: 64-66 wt.% SiO 2 ; 8-12 wt.% Al 2 O 3 ; 1-11 wt.% B 2 O 3 ; 0-5 wt.% Li 2 O; 6-12 wt.% Na 2 O; 1-4 wt% K 2 O; 0-4 wt.% MgO; 0-6 mol% CaO; and 0-2 wt.% ZrO 2 , where 20 mol% ⁇ R 2 O + R'O ⁇ 24 mol%; and 16 mol% ⁇ Al 2 O 3 + B 2 O 3 + ZrO 2 ⁇ 29 mol%.
• Table 1 lists non-limiting examples of silicate glass compositions of the present invention and their properties. Table 1
• SiO 2 which forms the matrix of the glass and is present in the inventive glasses in a concentration ranging from about 62 mol% up to and including about 70 mol%.
• SiO 2 serves as a viscosity enhancer that aids formability and imparts chemical durability to the glass. At concentrations that are higher than the range given above, SiO 2 raises the melting temperature prohibitively, whereas glass durability suffers at concentrations below the range. In addition, lower SiO 2 concentrations can cause the liquidus temperature to increase substantially in glasses having high alkali or alkali earth oxide concentrations.
• the greater alkali metal oxide content facilitates melting, softens the glass, enables ion exchange, decreases melt resistivity, and breaks up the glass network which increases thermal expansion and decreases durability. Mixtures of alkali metal oxides help depress the liquidus temperature and may enhance ion exchange as well. While Li 2 O provides fast ion exchange, low density, and high modulus, it is also quite expensive. Na 2 O is very desirable for ion exchange with K + ions for chemical strengthening and makes stable glasses with respect to devitrification. Small amounts of K 2 O relative to Na 2 O actually help increase the rate of K + for Na + ion exchange and decrease liquidus, but also increase the thermal expansivity of the glass.
• Alumina (Al 2 O 3 ) and, to a lesser extent, zirconia (ZrO 2 ) have the opposite effect of the alkali metal oxides.
• Al 2 O 3 scavenges NBOs to form AlO 4 tetrahedra while making the glass thermally harder.
• Alkaline earth oxides help create a steeper viscosity curve for the glasses. Replacing alkali metal oxides with alkaline earth metal oxides generally raise the anneal and strain points of the glass while lowering the melting temperatures needed to make high quality glass. MgO and CaO are less expensive than SrO and BaO and do not increase the density as much as the heavier oxides. BaO is also considered to be a hazardous or toxic material, and its presence is therefore undesirable. Accordingly, in one embodiment, the glass is substantially free of barium. Large amounts of MgO tend to increase the liquidus temperature, as the oxide is prone to form forsterite (Mg 2 SiO 4 ) at low MgO concentrations in sodium aluminosilicate glasses.
• forsterite Mg 2 SiO 4
• B 2 O 3 may be used as a flux to soften glasses, making them easier to melt.
• B 2 O 3 also helps scavenge non-bridging oxygen atoms (NBOs), which are created when the amount or concentration of modifiers exceeds that of Al 2 O 3 .
• NBOs non-bridging oxygen atoms
• B 2 O 3 converts the NBOs to bridging oxygen atoms through the formation of BO 4 tetrahedra, which increases the toughness of the glass by minimizing the number of weak NBOs.
• B 2 O 3 also lowers the hardness of the glass which, when coupled with the higher toughness, decreases the brittleness, thereby resulting in a mechanically durable glass.
• the alkali aluminosilicate glass described herein is substantially free of lithium.
• substantially free of lithium means that lithium is not intentionally added to the glass or glass raw materials during any of the processing steps leading to the formation of the alkali aluminosilicate glass. It is understood that an alkali aluminosilicate glass or an alkali aluminosilicate glass article that is substantially free of lithium may inadvertently contain small amounts of lithium due to contamination. The absence of lithium reduces poisoning of ion exchange baths, and thus reduces the need to replenish the salt supply needed to chemically strengthen the glass.
• the glass is compatible with continuous unit (CU) melting technologies such as the down-draw processes described above and the materials used therein, the latter including both fused zirconia and alumina refractories and zirconia and alumina isopipes.
• CU continuous unit
• the silicate glass comprises at least one alkali metal oxide and is ion exchangeable.
• ion-exchangeable is understood to mean that the glass is capable of being strengthened by ion exchange processes that are known to those skilled in the art. Such ion exchange processes include, but are not limited to, treating the heated alkali aluminosilicate glass with a heated solution containing ions having a larger ionic radius than ions that are present in the glass surface, thus replacing the smaller ions with the larger ions. Potassium ions, for example, could replace sodium ions in the glass.
• the down-drawn glass is chemically strengthened by placing it a molten salt bath comprising KNO 3 for a predetermined time period to achieve ion exchange.
• the temperature of the molten salt bath is about 430 0 C and the predetermined time period is about eight hours.
• the strength of the glass surface is controlled by the amount and size of surface flaws, a pristine surface that has had minimal contact has a higher initial strength.
• this high strength glass is then chemically strengthened, the resultant strength is higher than that of a surface that has been a lapped and polished.
• Chemical strengthening or tempering by ion exchange also increases the resistance of the glass to flaw formation due to handling.
• Down-drawn glass may be drawn to a thickness of less than about 2 mm.
• down drawn glass has a very flat, smooth surface that can be used in its final application without costly grinding and polishing.
• the down-drawable glass has a liquidus viscosity of at least 100 kpoise.
• the liquidus viscosity is at least 160 kpoise
• the liquidus viscosity is at least 220 kpoise.
• Surface compressive stress refers to a stress caused by the substitution during chemical strengthening of an alkali metal ion contained in a glass surface layer by another alkali metal ion having a larger ionic radius.
• potassium ions are substituted for sodium ions in the surface layer of the glass described herein.
• the glass has a surface compressive stress of at least about 200 MPa. In one embodiment, the surface compressive stress is at least about 600 MPa.
• the alkali aluminosilicate glass has a compressive stress layer that has a depth of at least about 30 ⁇ m and, in another embodiment, the depth of the compressive stress layer is at least about 40 ⁇ m.
• t is the thickness of the glass and DOL is the depth of exchange, also referred to as depth of layer.
• the glasses of the present invention tend to exhibit 200 Poise viscosities that are relatively high, between about 1500 0 C and 1675 0 C. Such viscosities are typical of industrial melting processes, and in some cases melting at such temperatures may be required to obtain glass with low levels of inclusions.
• Typical fining agents include, but are not limited to: oxides of arsenic, antimony, tin and cerium; metal halides (fluorides, chlorides and bromides); metal sulfates; and the like.
• Arsenic oxides are particularly effective fining agents because they release oxygen very late in the melt stage.
• arsenic and antimony are generally regarded as hazardous materials. Accordingly, in one embodiment, the glass is substantially free of antimony and arsenic, comprising less than about 0.05 wt% or about 0.05 mol% of each of the oxides of these elements.
• Tin (IV) oxide (SnO 2 ) and combinations of tin (FV) oxide with at least one of cerium (IV) oxide and halides are particularly useful as fining agents in the present invention.
• the glasses of the present invention have properties which are unexpected in light of the prior art. While soda lime silica glasses having decreased brittleness have been previously described, such glasses are neither fusion formable nor ion exchangeable to depths of layer of 20 ⁇ m. Moreover, the glasses of the prior art are not as hard as the glasses described herein. [0040] In addition to maximizing toughness, the silicate glasses described herein also allow hardness to be maximized without increasing brittleness. High levels of hardness provide greater scratch resistance. However, higher hardness increases brittleness unless toughness is correspondingly increased. Thus, if high levels of hardness can be accompanied by increased toughness, the resulting glass will have both increased scratch resistance and low brittleness. The silicate glass is resistant to both chipping and scratching, making it well suited for use in cover plates, touch screens, watch crystals, solar concentrators, windows, screens, containers, and other applications which require strong and tough glass with good scratch resistance.

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